I've currently got 4x 5870's in a rig, each connected using a modified 1x PCI-e extender to a GA-770T-D3L motherboard. PSU is a 1000watt Coolmaster SilentProM and is showing sub 650watt currently.

3 of them are connected into a 1x PCI-e slot and are recognised with lspci and run poclbm happily enough.

1 of them is connected into a 16x PCI-e slot. This does not show up with lspci.

I've not done much more investigation on this, but I was wondering, is using a 1x PCI-e extender from a 16x slot to a 16x card possible? I was sure it was. Is the motherboard being picky about the type of card in the slot?